A few years ago crude oil sold for about $3.00 a barrel and therefore did not attract the attention of thieves because a considerable amount of labor usually is involved in stealing crude oil. Moreover, an entire tank truck load of crude oil would only fetch $1,000.00-$2,000.00, and even after a tank truck load of crude oil had been stolen, it was often difficult to find someone to purchase the stolen goods. But times have changed and now a tank truck load of crude is worth $5,000.00-$8,000.00 and accordingly, crude oil theft is a worthwhile consideration of the more robust type of thief.
Out in the desolate west, crude continuously flows from an oil well into a stock tank. The tank may hold several truck loads of oil. A pumper drives about the isolated region, occasionally gauging and checking the level in the tanks. The pumper is sometimes negligent and fails to close the various incoming and outgoing flow lines properly. This oversight could result in thousands of dollars of crude being inadvertently transferred into a flow line and accordingly, the owner of the well would not be paid. It is also possible under these circumstances for a crude oil thief to transfer a tank truck load of oil from the stock tank into a transport truck without being noticed. This is especially so when the crude oil thief is associated with a pumper of the criminal type.
Most oil wells produce a considerable amount of sour gas. The sour gas migrates from the liquid contained within a stock tank and constitutes part of the vapor phase of the tank. In order to gauge a tank, the pumper opens a manhole, and drops a weighted flexible rule or tape to the bottom of the tank, and thereafter calculates the depth of the crude contained within the tank. After the pumper has opened the appropriate valves to transfer the crude oil from the tank into the sales oil line, he again gauges the tank and the difference in the measured liquid levels is used to calculate the payment to the owner of the oil well. This type of measurement depends to a large extent upon the care with which the pumper measures the tank contents.
Moreover, opening the manhole at the top of the tank is dangerous because it is always possible for sour gases containing hydrogen sulfide to be breathed by a pumper, thereby poisoning the pumper, which sometimes results in death.
Therefore, it would be desirable to have a measuring and recording apparatus which absolutely monitors and records the variable liquid level of a stock tank. It would also be desirable to be able to maintain an accurate record of this changing liquid level activity. It would especially be desirable to be able to monitor the fluid flow into and out of the tank without subjecting anyone to the deleterious effects of the sour gas contained within the gaseous phase of the stock tank. These desirable attributes are provided by the present invention.